One means of preparing a high-quality alumina is water hydrolysis of aluminum alkoxides. A convenient way of preparing the aluminum alkoxides involves preparing a mixture of high-molecular weight trialkyl aluminum by adding ethylene to triethyl aluminum (the well-known Ziegler process). The trialkyl aluminum is then oxidized to the corresponding aluminum alkoxides.
After removal of the alcohols resulting from the process the alumina is present in a slurry of water and alumina. A convenient means of removing the water from the slurry is by means of a spray dryer. Unfortunately, operating the spray dryer at high temperatures, as defined hereinafter, produces a discoloration of the alumina.
Similarly, maintaining the alumina at high temperatures, after drying and prior to bagging and shipping, results in a discoloration of the alumina.
We have found that addition of an inorganic oxidizing agent to the slurry, or to the alumina, as the case may be, substantially reduces this discoloration.